FIG. 4 is a partial cross-sectional view of prior art torque converter 200 with bushing 202 for piston 204. The torque converter includes torque converter clutch 206 with piston 204. The clutch is controllable, as is known in the art, to provide a torque path from cover 208 to output 210 engaged with input transmission shaft 212. The clutch is opened and closed by axially displacing piston 204 in response to fluid pressure in chambers 214 and 216. Typically, fluid pressure in the chambers is supplied by a pump in the transmission. In order to ensure proper function of the clutch, for example, to close the clutch with sufficient force to prevent unwanted slipping of the clutch, pressure in chamber 216 must be maintained at a sufficiently greater level than pressure in chamber 214. If the pressure in chamber 216 falls beyond a certain level, the pump must be operated to boost the pressure, increasing energy consumption for the transmission and reducing the efficiency associated with operation of the torque converter and transmission. One source for loss of pressure in chamber 216 is leakage from chamber 216 to chamber 214 via the interface of the bushing with the input shaft.
Typically, there is some degree of misalignment between cover 208, which is centered by flexplate 218, which in turn is centered by a crankshaft for an engine, and input shaft 212. Piston 204 is fixed to the cover by leaf spring 220 and thus, the centering action of the crankshaft is transferred to the piston. However, the piston also must interface with the input shaft, causing end 222 of the piston to be out of alignment with the shaft if the cover and shaft are misaligned. This misalignment can cause leakage between the two chambers.
It is known to fix a bushing, such as bushing 202, to the end of the piston to attempt to minimize leakage between pressure chambers for a clutch. Typically, the bushing is formed of aluminum or sheet steel coated with a friction reducing layer. The sealing function of the bushing is based on a small clearance between the bushing and the input shaft. The clearance however, needs to be large enough to allow for the misalignment, described above, between the cover and the input shaft. For torque converter 200, the clearance between the input shaft and the bushing depends on the alignment (or misalignment) between the piston (cover) and the input shaft. The alignment problem is exacerbated when the torque converter includes complex assemblies with a large stackup, which result in higher offsets, or tolerances, which require a large clearance between the input shaft and the piston/bushing. Since the bushing is fixed to the end of the piston, the bushing cannot adapt to the misalignment of the piston/bushing with respect to the input shaft, which increases the leakage past the interface of the bushing and the input shaft.
FIG. 5 is a partial cross-sectional view of prior art torque converter 300 with a groove and a seal 302 for piston 304. The torque converter includes torque converter clutch 306 with piston 304. The clutch is controllable, as is known in the art, to provide a torque path from cover 308 to output 310. The clutch is opened and closed by axially displacing piston 304 in response to fluid pressure in chambers 314 and 316. Typically, fluid pressure in the chambers is supplied by a pump in the transmission. In order to ensure proper function of the clutch, for example, to close the clutch with sufficient force to prevent unwanted slipping of the clutch, pressure in chamber 316 must be maintained at a sufficiently greater level than pressure in chamber 314. If the pressure in chamber 316 falls beyond a certain level, the pump must be operated to boost the pressure, increasing energy consumption for the transmission and reducing the efficiency associated with operation of the torque converter and transmission. One source for loss of pressure in chamber 316 is leakage from chamber 316 to chamber 314 via the interface of the bushing with the input shaft.
It is known use a seal, such as seal 302, to attempt to prevent this leakage. It is necessary to provide groove 318 in order to hold the seal in position. In general, it is not possible to directly engage the seal with the input shaft; therefore, an intermediate part such as hub 320 is provided between the seal and the input shaft. That is, the groove is formed in the hub. The configuration of FIG. 5 increases the size, cost, and complexity of torque converter 300 due to the addition of the hub. The seal is fixedly connected to the hub via the groove. Due to the resiliency of the seal, the seal can adapt to a limited degree to the misalignment of the piston/bushing with respect to the input shaft; however, the seal is essentially static with respect to the input shaft.